A large Gothic Franciscan basilica on the northeastern edge of the old city, balancing the Dominicans' San Domenico to the west. The plain brick exterior hides surviving frescoes by Pietro and Ambrogio Lorenzetti in the side chapels — fragments now, but enough to suggest what was lost when the rest of the church was redecorated in the 18th century.
The adjoining oratory of San Bernardino contains frescoes by Sodoma; the saint himself preached in the square outside, and the IHS monogram he popularised is still visible above the door.